Publicist Sarah Fuller did not mention bipolar disorder specifically Tuesday, but she noted in a statement Zeta-Jones "has said that she is committed to periodic care in order to manage her health in an optimum manner."

Rep. Jesse Jackson Jr. has also been diagnosed with bipolar II disorder. Jackson resigned from the House of Representatives last year after undergoing treatment. He later pleaded guilty to federal charges related to using campaign funds for personal expenses.

Bipolar II disorder "is a treatable condition that affects parts of the brain controlling emotion, thought and drive and is most likely caused by a complex set of genetic and environmental factors," according to the Mayo Clinic.

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It's a less severe condition than bipolar I, according to the Mayo Clinic. Bipolar II includes periods of depression alternated with hypomania, a mild form of mania that may include elevated mood and irritability. The depression periods usually last longer, the Mayo Clinic said.

In bipolar I, on the other hand, manic episodes can be "severe and dangerous," according to the Mayo Clinic. Some people experience psychosis, which encompasses delusions and hallucinations.

Bipolar episodes can be affected by seasonal changes, CNNHealth mental health expert Dr. Charles Raison wrote in 2011. People with unipolar depression tend to be less sensitive to changes in time, such as the lengths of day and night.

People with both kinds of depression may find relief in similar forms of psychotherapy, although the drug-based treatments for these disorders are different, Raison wrote last year.

Bipolar patients often don't respond well to antidepressants and do better on mood-stabilizing drugs or medications that reduce psychotic symptoms, Raison wrote. The drugs lithium and valproic acid are examples of mood stabilizers. Antipsychotics or anti-anxiety medications may also be helpful, depending on the patient.

Suicidal thoughts can be a feature of bipolar disorder. Hospitalization may be necessary in these cases, or if the patient is psychotic or behaving dangerously. Getting treatment at a hospital for a serious episode may be helpful as well. Some patients may also need substance abuse treatment.

If you are experiencing thoughts of suicide, call the National Suicide Prevention Lifeline at 800-273-8255.